U.S. Secretary of State John Kerry said Sunday terrorism must be opposed "with every fiber of our being."

Kerry, speaking Sunday at the Munich Security Conference, said the world is witnessing a form of "criminal anarchy." In a reference mainly to Islamic State militants, the top U.S. diplomat said there are no grounds to justify the rise in violent extremism.

He made the comments a day after Jordanian fighter jets struck Islamic State targets for a third straight day.

Jordan's air force chief said on Sunday his country's jet fighters had conducted 56 raids in three days of intensified bombing targeting a stronghold of Islamic State militants in northeast Syria.

UAE joins Jordan airstrikes

Jordan launched the bombing raids against the jihadist group's positions in Syria and Iraq on Thursday in response to its brutal killing of a captured Jordanian pilot, military action that it continued on Saturday.

An Islamic State video posted online this past week showed the pilot, Muath al-Kaseasbeh, locked in a cage, soaked with gasoline and burned alive while armed fighters watched.

There was no word of any new strikes against the militants on Sunday.

Meanwhile, the United Arab Emirates on Saturday ordered a squadron of F-16 fighter planes to Jordan to help with the airstrikes.

Both Jordan and the UAE are members of the U.S.-led coalition attacking the militants in their captured territory in Iraq and Syria.

General Mansour al Jbour, head of the Jordanian air force, said at a news conference, "We achieved what we aimed at. We destroyed logistics centers, arms depos and targeted hideouts of their fighters."

Jordan has carried out nearly 20 percent of the total sorties conducted by the U.S.-led coalition against Islamic State in Syria to date, al Jbour said, adding that they had been careful not to hit any civilians.

“We are determined to wipe them from the face of the Earth," he added.

US aid worker's fate unknown

Coalition airstrikes also continued Saturday, as the fate of an American aid worker held by Islamic State fighters remained unknown.

Kayla Mueller's family released a statement Friday saying they were still hopeful she is alive.

Their response came after the White House said it had seen no evidence to corroborate the militants' claim of her death by a recent Jordanian airstrike.

Skepticism over the claim comes after Jordanian authorities said their pilot was killed a month before IS released a video showing his death.

Mueller is the last remaining U.S. hostage known to be in the hands of the Islamic State group. Three other Americans held by the militants were beheaded.